Radioactive iodine therapy (RAI) for hyperthyroidism did not appear to increase the risk of all-cause cancer by any clinically significant amount, a new meta-analysis suggested.
The analysis, which pooled data from 12 studies involving nearly 500,000 patients with hyperthyroidism, found no significantly higher risk of any type of cancer in people exposed to RAI therapy compared to d ” other forms of therapy (standardized incidence ratio [SIR] 1.02, 95% CI 0.95-1.09), reported Won Jin Lee, MD, PhD, of Korea University College of Medicine in Seoul, and colleagues.
Patients treated with RAI also did not appear to have a significantly elevated risk of death from all cancers (standardized mortality ratio [SMR] 0.98, 95% CI 0.92-1.04), the researchers reported in JAMA network open.
However, the team said, when an analysis was done by specific cancer type, there was a link for thyroid cancer in particular – the only type of cancer to show this association. Specifically, patients with hyperthyroidism treated with RAI had a significantly elevated risk of thyroid cancer incidence (SIR 1.86, 95% CI 1.19-2.92) and cancer-related mortality. thyroid (SMR 2.22, 95% CI 1.37-3.59).
“One of the possible reasons could be the high dose of radiation exposure to the thyroid gland,” the researchers suggested, adding that one of the studies included in the meta-analysis mentioned that the average dose estimate organ for the thyroid gland in the Cooperative Thyrotoxicosis Treatment Follow-up Study was about 130 Gy – “a significantly greater dose than that given to other organs and tissues”.
“Underlying conditions of the thyroid gland could be another possible reason for the increased risk of malignant thyroid tumor after RAI for hyperthyroidism,” added Lee and his co-authors. “Thyroid-stimulating hormone and thyroid-stimulating antibody, present in Graves disease [GD], may play a role in carcinogenesis and tumor growth, and hyperthyroidism is associated with a high incidence of thyroid carcinoma. “
The relationship is also not surprising, as these particular patients already had abnormal thyroid function, the researchers added.
Other cancer sites assessed in the analysis included cancers of the digestive organs; eye; brain / central nervous system; lip, oral cavity and pharynx; respiratory and intrathoracic organs; Breast; genitals; urinary tract; lymphoid, hematopoietic and related tissue. RAI therapy was not significantly linked to an increased risk of malignant neoplasms at any of these cancer sites, the investigators said.
In a dose-response sub-analysis, only two of 12 studies included in the systematic review and meta-analysis found associations between a higher dose of RAI with breast cancer and solid cancer mortality (cancer mortality). breast for 370 MBq: 1.35, P= 0.03; solid cancer mortality for 370 MBq: 1.14, P= 0.01).
The author of a accompanying commentary, Bernadette Biondi, MD, of the University of Naples Federico II in Italy, called the results “reassuring” … and can be used to “reduce the anxiety of patients and clinicians about the risk of cancer after a RAI “.
She added that future studies examining the combination should include long-term follow-up and specifically compare RAI therapy with antithyroid drugs (ATD), which are the primary treatment for hyperthyroidism caused by MG.
“In Europe, about two-thirds of European Thyroid Association members prefer a first approach with ATD … However, RAI is the preferred first-line treatment for MG in the US and UK. United because it is associated with a higher cure rate and a lower relapse rate compared to ATD, ”explained Biondi.
And comparing these results with the three main treatment options currently available for hyperthyroidism – ATD, RAI therapy, and surgery – Biondi suggested paying special attention to subgroup analyzes, given the underlying etiology. hyperthyroidism, disease severity and cumulative effects. dose of RAI.
Lee’s group searched the PubMed, Cochrane and Embase databases for articles. A total of 12 studies were identified – representing a total of 479,452 patients – conducted in North America and Europe; nine were rated as high and medium quality, while three were rated relatively low or very low. The patients were treated between 1946 and 2015.
To be included in the meta-analysis, studies had to include patients treated for hyperthyroidism with RAI who were followed until cancer diagnosis or death. The studies also had to include at least one comparison group of patients not exposed to RAI treatment – for example, the general population, those treated for hyperthyroidism with thyroidectomy or DDA, or those exposed to different administered doses of RAI.
Among the limitations of the study, the team said, the individual studies included patients who were not randomized to the treatments received, and these observational studies may be vulnerable to confounding bias; and that the number of studies included in the quantitative review was relatively small to pool the risks of relatively rare cancer types despite the large cohort size and that only three studies had information on dose-response associations.
The study was funded by a grant from the National Research Foundation of Korea, funded by the Korea Ministry of Science and ICT.
Lee and his co-authors noted no conflicts of interest.
Biondi did not identify any conflict of interest.